Remove incorrect BIC/BBAN handling.

The BIC/BBAN handling code relied on assumptions that are valid for Dutch
IBAN's only. It would fail to correctly handle IBAN's for other participating
countries. Tear it out until I figure out a better way.
Tidy up constructor args checking.
Ignore whitespace better in doCalculateChecksum().

Step over space characters when transforming to numeric instead of compiling
regex, making a preparation pass and allocating a scrubbed string.
Add pom.xml fields for an eventual release to Maven.

Note that the groupId and artifactId have changed.
JavaDoc tweak.
Move the Modulo-97 calculation into a separate class.

It is a generic checksumming algorithm that shouldn't pollute the public API of
the IBAN type.
Improve code coverage.
Add getLengthForCountryCode(String).

This could be useful in form validation.
Add missing license header.
Add a package summary to the JavaDoc.
Add valueOf/parse to code sample, illustrate CharSequence better.
Add sample code and license to readme.
Markdown is not HTML, don't escape angle brackets.
Added the hamcrest-library to the maven test scope.